David Huang has shown off another effectively-zero-cost sensor, this time offering a high-resolution pressure sensor made from items you almost certainly already have lying around.
Huang has a knack for turning random objects into functional sensors: Earlier this week we highlighted a video in which he turns a piece of string into a functional tension sensor, simply by rubbing it against the lead of a pencil. Now, he's demonstrating another sensor made from household objects — and this one tracks pressure instead.
"The pressure sensor we can buy from outside is usually made from soft film. This type of sensor is usually higher in price," Huang explains in translation. "It may be about $10 or more according to the area of the sensor, and might require soldering. For newcomers, this might be very tricky."
The solution: As before, Huang has turned to the conductive properties of graphite from a pencil lead. "First, we need to find a soft foam material. In this video, we are using foam mat as the material," Huang explains. "I cut a small piece of the mat, then took a corrugated board and colored it with a pencil. Then we use the foam material that we just cut off to rub evenly on the corrugated board that we just colored with pencil and make one side of the material filled with graphite."
"Next, take two single-core wires. Strip the wire by about 3cm to make the copper wire exposed. Take a business card or harder cardboard, cut to about the size of the foam material and stick the single core wire on the card then stick the foam material with the graphite on the card by tape, and the sensor is done."
Like Huang's tension sensor, the pressure sensor works by expanding and contracting the graphite layer: Push on the foam and the graphite contracts, reducing its resistance; release the foam and the graphite expands again, increasing its resistance. Hooked up to the analogue input of any microcontroller, that data can then be used to determine pressure.
The full video is now available on Huang's YouTube channel.